Remove unused import in Enqueuer

Change-Id: Ifdd05ef69eebc1cc212c34cf9d5c25a9c5b3a940
diff --git a/src/main/java/com/android/tools/r8/shaking/Enqueuer.java b/src/main/java/com/android/tools/r8/shaking/Enqueuer.java
index 72b5c8c..4a358ee 100644
--- a/src/main/java/com/android/tools/r8/shaking/Enqueuer.java
+++ b/src/main/java/com/android/tools/r8/shaking/Enqueuer.java
@@ -161,7 +161,6 @@
 import com.android.tools.r8.utils.IteratorUtils;
 import com.android.tools.r8.utils.ListUtils;
 import com.android.tools.r8.utils.OptionalBool;
-import com.android.tools.r8.utils.Pair;
 import com.android.tools.r8.utils.SetUtils;
 import com.android.tools.r8.utils.StringDiagnostic;
 import com.android.tools.r8.utils.ThreadUtils;